Zinc and copper retention during pregnancy: the adequacy of prenatal diets with and without dietary supplementation

Twenty-four pregnant women, in their second trimester, participated in two seven-day metabolic experiments to evaluate zinc and copper utilization from self-selected diets, with or without supplementation. Recommended dietary allowances for zinc or suggested intakes for copper were not met unless supplements of these nutrients were consumed. Zinc retentions in the unsupplemented group were 1.9 and 0.3 mg/day during the first and second metabolic periods, respectively. Zinc retentions in the supplemented group were 2.3 and 4.7 mg/day during the same two periods. Intakes above 8 mg/day resulted in positive retentions. Based on individual variation, however, intakes of 20 mg/day, the current RDA, would not be excessive although possibly some level between these two extremes would be adequate. Copper retentions in the unsupplemented and supplemented groups combined over the two balance periods were −0.02 and 0.89 mg/day, respectively. Adequate copper retention does not appear possible without the use of a supplement.